A virtual synchronization optimization control method for grid-connected inverters suitable for transient support

Abstract

The present invention proposes a virtual synchronous optimization control method for a grid-connected inverter suitable for transient support of a power grid. First, a control model based on a virtual synchronous type grid-connected converter is established, and based on the control model, a first power angle boundary for considering transient synchronous stability and a second power angle boundary for considering small signal stability and fault current limiting are obtained; a voltage boundary for considering fault current limiting is obtained according to the first power angle boundary and the second power angle boundary; based on the power angle boundary and the voltage boundary, optimal active power compensation, optimal reactive power compensation and target active power and target voltage parameters for optimal transient synchronous stability are respectively obtained; when the grid voltage sags, the reactive loop is frozen, and an active reference signal and a voltage reference signal are adaptively given to enhance the synchronous stability and fault current suppression capability of the virtual synchronous type grid-connected converter, which is beneficial to evaluating the power support capability of the converter during a grid fault.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and in particular relates to a virtual synchronization optimization control method for a grid-connected inverter suitable for transient support. Background Art

[0002] With the rapid development of renewable energy such as wind power and photovoltaics, the penetration rate of power electronic converters, which are important interfaces for new energy grid connection, in the power system continues to increase, and the development of modern power systems has gradually shown a "double high" trend.

[0003] As the interface between new renewable energy generation units and the power grid, the grid-connected converter plays an important role in reactive power compensation, harmonic control, etc. The control strategy of the grid-connected converter can be divided into two types according to its phase synchronization method: grid-building control and grid-following control. Under grid-following control, the grid-connected converter mainly operates in the form of a current source. The grid voltage phase is extracted by adopting a single synchronous coordinate system phase-locked loop to sample the PCC point voltage of the grid-connected converter. Under the action of the current inner loop, the current reference is directly given, so that the grid-connected converter can achieve constant current operation on the AC side. The operating voltage and phase of the grid-connected converter are completely supported by the power grid.

[0004] Grid-following control has the following main defects during power grid faults: First: under grid-following control, the grid-connected converter can only be supported by the grid in terms of frequency and voltage. However, under fault conditions, it is difficult for the grid to maintain its own voltage and frequency stability. Therefore, grid-following control is difficult to provide voltage and frequency support for the faulty grid; Second: under grid-following control, due to the integrator action of the phase-locked loop, partial negative damping is introduced into the closed-loop system of the grid-connected converter, which is equivalent to introducing additional kinetic energy into the system, which can easily lead to synchronization instability problems in the system.

[0005] Grid-connected converters do not need to use phase-locked loops to extract grid phase. They can automatically generate their own frequency and voltage references based on the active and reactive power output by the grid-connected converter to achieve synchronous operation with the grid. Virtual synchronous machine control can achieve synchronous operation with the grid by simulating the rotor motion and droop characteristics of the synchronous generator. It has strong robustness in providing voltage and frequency support for the grid under transient grid faults. However, due to its own strong inertia, the traditional virtual synchronous machine still faces the problem of synchronous instability during grid faults.

[0006] On the other hand, the current resistance of the power electronic devices inside the grid-connected converter is often designed to be 1.5-2 times the current resistance limit, while traditional synchronous generators can withstand 4-8 times the rated current. Therefore, during a grid fault, the overcurrent problem of the grid-connected converter is very serious. Long-term overcurrent can easily cause the converter to overheat and burn out.

[0007] The above content is only used to assist in understanding the technical solution of the present invention and does not constitute an admission that the above content is prior art. Summary of the Invention

[0008] To solve the above technical problems mentioned in the background art, the present invention proposes a virtual synchronization optimization control method for a grid-connected inverter suitable for transient support, the method comprising:

[0009] Step S10: Establishing a control model for a virtual synchronous grid-connected converter; obtaining a first power angle boundary for considering transient synchronous stability based on the control model; obtaining a second power angle boundary for considering small signal stability and fault current limiting based on the control model; determining a target power angle boundary based on the first power angle boundary and the second power angle boundary; and obtaining a voltage boundary for considering fault current limiting based on the target power angle boundary.

[0010] Step S20: Based on the target power angle boundary and the voltage boundary, respectively, target active power and target voltage parameters for optimal active power compensation, optimal reactive power compensation, and optimal transient synchronization stability are obtained; when the grid voltage sags, the reactive power loop is frozen, and an active reference signal corresponding to the target active power and a voltage reference signal corresponding to the target voltage parameter are adaptively given to enhance the synchronization stability and fault current suppression capability of the virtual synchronous type grid-connected converter.

[0011] Preferably, the step of establishing a control model based on a virtual synchronous type grid-connected converter in step S10 specifically includes:

[0012] Step S11: establishing a control model based on a virtual synchronous grid-connected converter, wherein the control model at least includes an active loop model, a reactive loop control model, an instantaneous active power model, and a reactive power calculation model;

[0013] The active loop model is expressed by the following formula 1:

[0014]

[0015] In the above formula 1, J is the virtual inertia of the converter, D is the virtual damping coefficient of the converter, and P ref is the given active power reference value, P e is the converter output active power, t is time, δ is the converter virtual power angle, ω N is the rated output angular frequency of the converter;

[0016] The reactive loop control model is expressed by the following equation 2:

[0017] Q ref -Q e =-k q(U N -U * ) (Formula 2)

[0018] In the above formula 2, Q ref The reactive power reference value is given to the converter, Q e is the reactive power output by the converter, k q is the voltage-reactive power droop coefficient, U N is the rated output phase voltage amplitude of the converter,

[0019] U * It is the reference of the output phase voltage amplitude of the converter;

[0020] The instantaneous active power model is expressed by the following equation 3:

[0021]

[0022] In the above formula 3, R g is the equivalent resistance of the circuit, X g is the line equivalent reactance, U g is the grid phase voltage amplitude, U is the actual output phase voltage amplitude of the converter;

[0023] The reactive power calculation model is expressed by the following formula 4:

[0024]

[0025] In the above formula 4, R g is the equivalent resistance of the circuit, X g is the line equivalent reactance, U g is the grid phase voltage amplitude, and U is the actual output phase voltage amplitude of the converter.

[0026] Accordingly, the first power angle boundary includes the power angle upper boundary δ for considering transient synchronous stability max1 and the lower bound δ min1 The second power angle boundary includes the power angle upper boundary δ for considering small signal stability and fault current limiting max2 and the lower bound δ min2 ;

[0027] Preferably, the step of acquiring the first power angle for considering transient synchronous stability based on the control model in step S10 specifically includes:

[0028] Step S12: Based on the control model, the upper bound of the power angle δ for considering transient synchronous stability is obtained respectively. max1 and the lower bound δ min1 , are obtained using the following (Formula 5) and (Formula 6) respectively.

[0029]

[0030]

[0031] Accordingly, the step of obtaining the second power angle boundary for considering small signal stability and fault current limiting based on the control model in step S10 specifically includes:

[0032] Step S13: Based on the control model, the voltage after the grid drops is recorded as U gF , the line impedance is recorded as R g With X g , the converter design rated current I N , respectively calculate the upper boundary of the power angle δ for considering small signal stability and fault current limiting max2 With the lower boundary δ min2 ; Consider 1.5 times the fault current limit,

[0033] If there is

[0034]

[0035] Then the upper power angle limit of the second power angle boundary is calculated as

[0036]

[0037] δ min2 =0 (Formula 9)

[0038] like

[0039]

[0040] but

[0041]

[0042] δ min2 =0 (Equation 12)

[0043] Accordingly, the step of determining the target power angle boundary based on the first power angle boundary and the second power angle boundary in step S10 specifically includes:

[0044] Step S14: Obtain the intersection based on the above results to obtain the upper and lower boundaries of the target power angle.

[0045] δ max =min{δ max1 , δ max2 (Equation 13)

[0046] δ min =max{δ min1 , δ min2 (Equation 14)

[0047] Wherein, the formula 13 is used to represent the upper limit of the target power angle, and the formula 14 is used to represent the lower limit of the target power angle.

[0048] Preferably, the step of obtaining a voltage boundary for considering fault current limiting according to the target power angle boundary specifically includes:

[0049] Step S15: Calculate the voltage boundary based on the target power angle boundary obtained in step S13, as shown in the formulas:

[0050] U min =U gF cosδ,δ∈[δ min ,δ max ] (Equation 15)

[0051]

[0052] Wherein, the formula 15 is used to represent the upper boundary of the voltage boundary, and the formula 16 is used to represent the lower boundary of the voltage boundary.

[0053] Preferably, the step S20 specifically includes:

[0054] Step S21: Obtain the optimal control parameters for transient synchronous stability, and record the steady-state power angle before the grid voltage sag as δ a , the steady-state power angle after the grid voltage drops is recorded as δ b , the grid voltage before the fault is recorded as U gN , the line impedance module is recorded as R; the reactive power control loop is directly controlled by U *(0+) Instead, the active power reference in the active loop switches to P ref (0+) , the above parameters are obtained by (Equation 17), (Equation 18), (Equation 19), and (Equation 20) respectively:

[0055]

[0056]

[0057]

[0058]

[0059] Step S22: Obtain optimal control parameters for reactive power compensation. The reactive power loop is frozen during grid sag. The voltage reference U * byU *(0+) Direct replacement, the active power reference in the active loop is switched to P ref (0+), the above parameters are calculated by (Equation 21) and (Equation 22) respectively:

[0060]

[0061]

[0062] Step S23: Obtain the optimal control parameters for active power compensation, process the reactive loop, obtain the equation of active power only with respect to the power angle, and obtain the power angle δ at the maximum active power point by derivative. pmax , and compare the upper bound of the power angle to find the minimum value of the two, and obtain the optimal power angle point δ of active compensation considering the parameter boundary. *(0+) , bring the power angle back to the voltage calculation formula to get U *(0+) , the active power reference in the active loop switches to P at the transient moment ref (0+) , which can be calculated by formula 25:

[0063]

[0064] δ *0+ =min{δ max ,δ Pmax} (Equation 24)

[0065]

[0066] The beneficial effects of the present invention are: first, by establishing a control model of a virtual synchronous type grid-connected converter, the power angle and voltage reference boundaries for considering transient synchronization stability and fault current limiting are obtained, ensuring that synchronization stability and fault current limiting are taken into account when the grid voltage is temporarily reduced. Based on this parameter boundary, an adaptive control strategy with optimal active power compensation, optimal reactive power compensation and optimal transient synchronization stability is obtained, which is conducive to evaluating the power compensation capability of the converter during a grid fault, improving the synchronization stability and fault current suppression capability of the converter during a grid fault, and maximizing the current-carrying capacity of the device to maximize the power compensation capability of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 This is a flow chart of a virtual synchronization optimization control method for a grid-connected inverter suitable for transient support according to the present invention;

[0068] Figure 2 A schematic diagram of the main circuit topology of a virtual synchronous machine controlled grid-connected converter according to the present invention;

[0069] Figure 3 A control loop block diagram of a virtual synchronous machine controlled grid-connected converter in the system of the present invention;

[0070] Figure 4 It is a schematic diagram of the installation of the present invention;

[0071] Figure 5 This is a comparison chart of the stability and fault current suppression improvement effects of the present invention. DETAILED DESCRIPTION

[0072] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0073] In order to solve the above problems, the present invention first proposes a technical solution that considers both transient synchronization stability and fault current suppression parameter feasible domain. Figure 2 As shown, the control loop block diagram is as follows Figure 3 As shown in the figure, by freezing the reactive loop when the grid voltage sags, and by directly adaptively setting the active reference signal and voltage reference signal, the synchronization stability and fault current suppression capability of the virtual synchronous grid-connected converter are enhanced.

[0074] It's understandable that grid-connected converters can provide voltage and frequency support to the grid compared to grid-following converters. Virtual synchronous generator-based grid-connected converters, by simulating the synchronous generator rotor equation and reactive power-voltage droop characteristics, can automatically achieve phase synchronization with the grid, eliminating the need for an additional phase-locked loop (PLL) design. However, during grid voltage sags, the rotor inertia characteristics simulated by the virtual synchronous generator pose a risk of synchronous instability. Furthermore, because grid-connected converters utilize power electronic devices such as silicon or silicon carbide MOSFETs or IGBTs, their designed current handling capacity is often 1.5-2 times the rated current, while traditional synchronous generators can withstand 4-8 times the short-circuit current. Therefore, during grid voltage sags, grid-connected converters using traditional virtual synchronous generator control face the dual risks of device overcurrent, overheating, and synchronous instability.

[0075] This embodiment of the present invention first calculates the power angle and voltage reference boundary conditions required to achieve transient synchronous stability and overcurrent limitation during a grid voltage sag. Based on this, the cross-coupling between the active and reactive loops is eliminated by directly freezing the reactive loop during a grid fault. Subsequently, three adaptive control strategies are designed to achieve optimal active power compensation, optimal reactive power compensation, and optimal transient synchronous stability. This method addresses the issue of balancing transient synchronous stability with fault overcurrent, enhancing the converter's synchronous stability and fault current suppression capabilities during grid faults. It helps engineers evaluate the converter's power compensation capabilities, avoids the use of additional short-circuit current limiting hardware devices such as circuit breakers, reduces equipment costs, and offers advantages such as ease of installation and maintenance and low equipment requirements.

[0076] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings.

[0077] Step 1: First, establish a control model for a virtual synchronous grid-connected converter, derive a first power angle boundary that considers transient synchronous stability, and a second power angle boundary that considers fault current limiting and small signal stability. Then, determine the target power angle boundary based on the first and second power angle boundaries; obtain the voltage boundary for considering fault current limiting based on the target power angle boundary; the first power angle boundary includes the upper power angle boundary δ for considering transient synchronous stability. max1 and the lower bound δ min1 The second power angle boundary includes the power angle upper boundary δ for considering small signal stability and fault current limiting max2 and the lower bound δ min2 ;

[0078] The main circuit topology involved in this embodiment is as follows Figure 2 As shown, the control method is as follows Figure 1 As shown, the first step of the optimization control method of this embodiment includes the following steps:

[0079] Step S11: first, establishing a control model based on a virtual synchronous grid-connected converter, wherein the control model at least includes an active loop model, a reactive loop control model, an instantaneous active power model, and a reactive power calculation model;

[0080] The active loop model is expressed by the following formula 1:

[0081]

[0082] In the above formula 1, J is the virtual inertia of the converter, D is the virtual damping coefficient of the converter, and P ref is the given active power reference value, P eis the converter output active power, t is time, δ is the converter virtual power angle, ω N is the rated output angular frequency of the converter;

[0083] The reactive loop control model is expressed by the following equation 2:

[0084] Q ref -Q e =-k q (U N -U * ) (Formula 2)

[0085] In the above formula 2, Q ref The reactive power reference value is given to the converter, Q e is the reactive power output by the converter, k q is the voltage-reactive power droop coefficient, U N is the rated output phase voltage amplitude of the converter, U * It is the reference of the output phase voltage amplitude of the converter;

[0086] The instantaneous active power model is expressed by the following equation 3:

[0087]

[0088] In the above formula 3, R g is the equivalent resistance of the circuit, X g is the line equivalent reactance, U g is the grid phase voltage amplitude, U is the actual output phase voltage amplitude of the converter; it is usually considered that U=U * ;

[0089] The reactive power calculation model is expressed by the following formula 4:

[0090]

[0091] In the above formula 4, R g is the equivalent resistance of the circuit, X g is the line equivalent reactance, U g is the grid phase voltage amplitude, U is the actual output phase voltage amplitude of the converter; it is usually considered that U=U * .

[0092] Step S12: Based on the control model, the upper bound of the power angle δ for considering transient synchronous stability is obtained respectively. max1 and the lower bound δ min1 , are obtained using the following (Formula 5) and (Formula 6) respectively.

[0093]

[0094]

[0095] Step S13: Based on the control model, the voltage after the grid drops is recorded as U gF , the line impedance is recorded as R g With X g , the converter design rated current I N , respectively calculate the upper boundary of the power angle δ for considering small signal stability and fault current limiting max2 With the lower boundary δ min2 ; Consider 1.5 times the fault current limit,

[0096] If there is

[0097]

[0098] Then the upper power angle limit of the second power angle boundary is calculated as

[0099]

[0100] δ min2 =0 (Formula 9)

[0101] like

[0102]

[0103] but

[0104]

[0105] δ min2 =0 (Equation 12)

[0106] Step S14: Obtain the intersection based on the above results to obtain the upper and lower boundaries of the target power angle.

[0107] δ max =min{δ max1 , δ max2 (Equation 13)

[0108] δ min＝max {δ min1 , δ min2 (Equation 14)

[0109] Wherein, the formula 13 is used to represent the upper limit of the target power angle, and the formula 14 is used to represent the lower limit of the target power angle.

[0110] Step S15: Calculate the voltage boundary based on the target power angle boundary obtained in step S13, as shown in the formulas:

[0111] U min =U gF cosδ,δ∈[δ min,δ max ] (Equation 15)

[0112]

[0113] Wherein, the formula 15 is used to represent the upper boundary of the voltage boundary, and the formula 16 is used to represent the lower boundary of the voltage boundary.

[0114] Step 2: Based on the target power angle boundary and the voltage boundary, respectively obtain the target active power and target voltage parameters for optimal active power compensation, optimal reactive power compensation, and optimal transient synchronous stability:

[0115] Step S21: Obtain the optimal control parameters for transient synchronous stability, and record the steady-state power angle before the grid voltage sag as δ a , the steady-state power angle after the grid voltage drops is recorded as δ b , the grid voltage before the fault is recorded as U gN , the line impedance module is recorded as R; the reactive power control loop is directly controlled by U *(0+) Instead, the active power reference in the active loop switches to P ref (0+) , the above parameters are obtained by (Equation 17), (Equation 18), (Equation 19), and (Equation 20) respectively:

[0116]

[0117]

[0118]

[0119]

[0120] Step S22: Obtain optimal control parameters for reactive power compensation. The reactive power loop is frozen during grid sag. The voltage reference U * byU *(0+) Direct replacement, the active power reference in the active loop is switched to P ref (0+) , the above parameters are calculated by (Equation 21) and (Equation 22) respectively:

[0121]

[0122]

[0123] Step S23: Obtain the optimal control parameters for active power compensation, process the reactive loop, obtain the equation of active power only with respect to the power angle, and obtain the power angle δ at the maximum active power point by derivative. pmax, and compare the upper bound of the power angle to find the minimum value of the two, and obtain the optimal power angle point δ of active compensation considering the parameter boundary. *(0+) , bring the power angle back to the voltage calculation formula to get U *(0+) , the active power reference in the active loop switches to P at the transient moment ref (0+) , which can be calculated by formula 25:

[0124]

[0125] δ *0+ =min{δ max ,δ Pmax} (Equation 24)

[0126]

[0127] In the specific implementation, Figure 4 As shown in the figure, in the virtual synchronous type grid-connected converter, the transient process directly freezes the reactive loop, and the voltage reference is U *(0+) Directly given, the active power reference of the active loop is given by P ref (0+) The specific three modes are determined by the power demand given by the grid dispatcher.

[0128] like Figure 5 The figure shows the virtual power angle, grid output current, active power waveform, and reactive power waveform of the traditional virtual synchronous type grid-connected converter during the transient period of grid voltage drop. In the figure, δ is the virtual power angle, I is the grid current, and P e is the active power, Q e is reactive power. When the control strategy proposed by the present invention is adopted, the converter does not experience synchronous instability and overcurrent. When the control strategy proposed by the present invention is not adopted, the converter experiences synchronous instability and overcurrent. At the same time, it can be seen from the waveforms that when the control strategy with the best active power transmission is adopted, the active power that the converter can output is the largest among all control strategies. When the control strategy with the best reactive power transmission is adopted, the reactive power that the converter can output is the largest among all control strategies. When the control strategy with the best transient synchronous stability is adopted, the converter power angle hardly changes, and the transient process is the shortest among all control strategies.

[0129] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A virtual synchronization optimization control method for grid-connected inverters suitable for transient support, characterized in that: The method comprises the following steps: Step S10: Establishing a control model for a virtual synchronous grid-connected converter; obtaining a first power angle boundary for considering transient synchronous stability based on the control model; obtaining a second power angle boundary for considering small signal stability and fault current limiting based on the control model; determining a target power angle boundary based on the first power angle boundary and the second power angle boundary; and obtaining a voltage boundary for considering fault current limiting based on the target power angle boundary. Step S20: Based on the target power angle boundary and the voltage boundary, respectively, obtaining target active power and target voltage parameters for optimal active power compensation, optimal reactive power compensation, and optimal transient synchronization stability; freezing the reactive loop when the grid voltage sags, and adaptively providing an active reference signal corresponding to the target active power and a voltage reference signal corresponding to the target voltage parameter to enhance the synchronization stability and fault current suppression capability of the virtual synchronous grid-connected converter; Wherein, the step S20 specifically includes: Step S21: Obtain the optimal control parameters for transient synchronous stability, and record the steady-state power angle before the grid voltage sag as δ a , the steady-state power angle after the grid voltage drops is recorded as δ b , the grid voltage before the fault is recorded as U gN , the line impedance module is recorded as R; the reactive power control loop is directly controlled by U *(0+) Instead, the active power reference in the active loop switches to P ref (0+) , the above parameters are obtained by (Equation 17), (Equation 18), (Equation 19), and (Equation 20) respectively: Step S22: Obtain optimal control parameters for reactive power compensation. The reactive power loop is frozen during grid sag. The voltage reference U * byU *(0+) Direct replacement, the active power reference in the active loop is switched to P ref (0+) , the above parameters are calculated by (Equation 21) and (Equation 22) respectively: Step S23: Obtain the optimal control parameters for active power compensation, process the reactive loop, obtain the equation of active power only with respect to the power angle, and obtain the power angle δ at the maximum active power point by derivative. pmax , and compare the upper bound of the power angle to find the minimum value of the two, and obtain the optimal power angle point δ of active compensation considering the parameter boundary. *(0+) , bring the power angle back to the voltage calculation formula to get U *(0+) , the active power reference in the active loop switches to P at the transient moment ref (0+) , which can be calculated by formula 25: d *0+ =min{δ max ,d Pmax } (expression24) 2. The method according to claim 1, wherein The step of establishing a control model based on a virtual synchronous type grid-connected converter in step S10 specifically includes: Step S11: establishing a control model based on a virtual synchronous grid-connected converter, wherein the control model at least includes an active loop model, a reactive loop control model, an instantaneous active power model, and a reactive power calculation model; The active loop model is expressed by the following formula 1: In the above formula 1, J is the virtual inertia of the converter, D is the virtual damping coefficient of the converter, and P ref is the given active power reference value, P e is the converter output active power, t is time, δ is the converter virtual power angle, ω N is the rated output angular frequency of the converter; The reactive loop control model is expressed by the following equation 2: Q ref -Q e = -k q (U N -U * ) (Equation 2) In the above formula 2, Q ref The reactive power reference value is given to the converter, Q e is the reactive power output by the converter, k q is the voltage-reactive power droop coefficient, U N is the rated output phase voltage amplitude of the converter, U * It is the reference of the output phase voltage amplitude of the converter; The instantaneous active power model is expressed by the following equation 3: In the above formula 3, R g is the equivalent resistance of the circuit, X g is the line equivalent reactance, U g is the grid phase voltage amplitude, U is the actual output phase voltage amplitude of the converter; The reactive power calculation model is expressed by the following formula 4: In the above formula 4, R g is the equivalent resistance of the circuit, X g is the line equivalent reactance, U g is the grid phase voltage amplitude, and U is the actual output phase voltage amplitude of the converter.

3. The method according to claim 2, wherein The first power angle boundary includes an upper power angle boundary δ for considering transient synchronous stability. max1 and the lower bound δ min1 The second power angle boundary includes the power angle upper boundary δ for considering small signal stability and fault current limiting max2 and the lower bound δ min2 ; Accordingly, the step of acquiring the first power angle for considering transient synchronous stability based on the control model in step S10 specifically includes: Step S12: Based on the control model, the upper bound of the power angle δ for considering transient synchronous stability is obtained respectively. max1 and the lower bound δ min1 , respectively, are obtained using the following (Formula 5) and (Formula 6); Accordingly, the step of obtaining the second power angle boundary for considering small signal stability and fault current limiting based on the control model in step S10 specifically includes: Step S13: Based on the control model, the voltage after the grid drops is recorded as U gF , the line impedance is recorded as R g With X g , converter design rated current I N , respectively calculate the upper boundary of the power angle δ for considering small signal stability and fault current limiting max2 With the lower boundary δ min2 ; Consider 1.5 times the fault current limit, If there is Then the upper limit of the power angle of the second power angle boundary is calculated as δ min2 =0 (Formula 9) like but δ min2 =0 (Equation 12) Accordingly, the step of determining the target power angle boundary based on the first power angle boundary and the second power angle boundary in step S10 specifically includes: Step S14: Obtain the intersection based on the above results to obtain the upper and lower boundaries of the target power angle. d max =min{δ max1 , d max2 } (expression13) d min =max{δ min1 , d min2 } (expression14) Wherein, the formula 13 is used to represent the upper limit of the target power angle, and the formula 14 is used to represent the lower limit of the target power angle.

4. The method according to claim 3, wherein The step of obtaining a voltage boundary for considering fault current limiting according to the target power angle boundary specifically includes: Step S15: Calculate the voltage boundary based on the target power angle boundary obtained in step S13, as shown in the formulas: U min = U gF cosδ, δ ∈ [δ min , δ max (Equation 15) Wherein, the formula 15 is used to represent the upper boundary of the voltage boundary, and the formula 16 is used to represent the lower boundary of the voltage boundary.

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